New insight into the mechanism of peroxymonosulfate activation by sulfur-containing minerals: Role of sulfur conversion in sulfate radical generation

Abstract

Peroxymonosulfate (PMS) or persulfate activation by sulfur-containing minerals has been applied extensively for the degradation of contaminants; however, the role of sulfur conversion in this process has not been fully explored. In this study, pyrite (FeS2)-based PMS activation process was developed for diethyl phthalate (DEP) degradation, and its underlying mechanisms were elucidated. PMS was found to be efficiently activated by FeS2 for DEP degradation and mineralization, achieving 58.9% total organic carbon removal using 0.5 g/L FeS2 and 2.0 mM PMS. Sulfides were the dominant electron donor for PMS activation, and mediated Fe(II) regeneration to activate PMS on the surface of FeS2 particles. Meanwhile, different sulfur conversion intermediates, such as S52−, S80, S2O32−, and SO32−, were formed from the oxidation of sulfides by Fe(III) and PMS, and determined by X-ray photoelectron spectroscopy and in-situ attenuated total reflectance Fourier transform infrared spectroscopy analysis. SO32− was the dominant sulfur species responsible for sulfate radicals (SO4−) generation by activating PMS directly or activating Fe(III) to initiate a radical chain reaction, which was supported by the electron paramagnetic resonance results. This study highlights the important role of sulfur conversion in PMS activation by pyrite and provides new insights into the mechanism of oxidant activation by sulfur-containing minerals.